Fruit maturity . The characteristics of a fruit surface may change during 

 maturation. Thus, fruit maturity might affect solution uptake and development 

 of spots after storage. We harvested Mcintosh early-, mid-, and late-season 

 (at 1-week intervals) from the same trees and dipped them in a series of CaCl2 

 solutions with and without diphenylamine (DPA) . Fruit maturity had no effect 

 on the amount of fruit spotting resulting from these treatments. Thus, 

 maturity does not appear to be a significant factor in development of spotting. 



Addition of DPA . DPA increases Ca uptake from a solution when combined 

 with CaCl2, as is normally recommended. Why this occurs has not been 

 established. To find out if DPA increased spotting from Ca treatments we 

 compared two different CaCl2 concentrations, with and without DPA. We found 

 that DPA tripled the amount of spotting resulting from a given CaCl2 

 concentration. We also found that DPA alone caused significant spotting on 

 Mcintosh, especially around the calyx area. Why DPA increases spotting is 

 unclear. We tried two different formulations of DPA and got equivalent amounts 

 of spotting, with and without CaCl2. The recommended rate of CaCl2 use for 

 postharvest treatments may have to vary, depending on whether or not DPA is 

 included in the mixture. It should be noted that a number of fruit that were 

 treated with neither CaCl2 nor DPA developed some spotting after storage, 

 apparently as a result of latent damage to cells caused by orchard applications 

 of pesticides. (These trees had not been sprayed with foliar CaCl2.) Clearly, 

 not all spotting of fruit after storage is attributable to CaCl2 or DPA. 



To follow up on these findings, in 1985-86 we conducted a large test in 

 which we dipped Mcintosh in solutions containing 4, 8, 12, or 16 lbs of CaCl2 

 per 100 gallons plus DPA, a surfactant, or neither of these materials. After 

 storage we measured both the increase of Ca in the fruit and the amount of 

 fruit spotting. As expected, both Ca uptake and fruit spotting increased in a 

 straight line as the concentration of CaCl2 in the dip solution increased. The 

 presence of DPA in the dipping solution did not increase the amount of Ca in 

 the fruit at the end of storage, but it increased the amount of spotting. Use 

 of the surfactant also had no effect on the final amount of Ca in the fruit, 

 but increased the amount of spotting, though to a lesser extent than did DPA. 



Washing fruit after dipping . A report from Australia stated that treated 

 apples could be washed 3 days after dipping or drenching; the wash reduced 

 spotting but not total Ca uptake. To test this approach, we dipped Mcintosh in 

 12 lbs of CaCl2 per 100 gallons, washed them 1, 3, or 7 days after dipping, and 

 measured Ca uptake and spotting at the end of storage as compared with similar 

 samples that had not been washed. Washing 1 or 3 days after dipping greatly 

 reduced Ca uptake, while washing 7 days after dipping produced less of a 

 reduction. In this experiment CaCl2 did not increase spotting, whether or not 

 the fruit were washed. It appears that even if washing controlled spotting, 

 washing 3 days or less after dipping would nearly eliminate any benefit from 

 treating with CaCl2. Furthermore, the logistics of washing after dipping could 

 make this approach prohibitively time-consuming under our storage systems. 



Interaction with iron . At a meeting last summer, a colleague from 

 Australia said that the cause of spotting was actually iron, which was 

 extracted from metal and put into solution by the CaCl2. At the same meeting, 

 a report from New Jersey indicated that presence of iron in water was the cause 

 of damage to peaches following hydrocooling. Thus, we conducted an experiment 

 to test the possible role of iron in apple spotting. 



